1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus for recording video and audio information on a magnetic tape in a helically scanning system.
2. Description of the Related Art
For accurately recording a digital video signal and a digital audio signal by a digital video tape recorder, it has hitherto necessary to confirm the state of recording by reproducing the recorded data soon after recording, namely, to perform simultaneous monitoring.
(1) First Prior Art PA1 (2) Second Prior Art PA1 (3) Third Prior Art PA1 (4) Fourth Prior Art PA1 (5) Fifth Prior Art
FIG. 41 of the accompanying drawings shows a prior digital video tape recorder disclosed in, for example, Japanese Patent Publication No. 40789/1987.
In FIG. 41, reference numerals 1-1,1-2 designate a pair of rotary magnetic heads. These two rotary magnetic heads 1-1, 1-2 are supported by an electric strain element, as shown FIGS. 42 and 43. The electric strain element is a bimorph plate 3-1. The magnetic head 1-1 is attached to one end of the bimorph plate 3-1, and the other end of the bimorph plate 3-1 is attached to a base plate 5 by an adhesive 4. A damper member 6 is disposed between the base plate 5 and the bimorph plate 3-1.
In this case, when a voltage is applied to the bimorph plate 3-1, a direction of polarization of the bimorph plate 3-1 is selected in such a manner that the head 1-1 is moved laterally of the track, as indicated by the arrow 7, according to the polarity and level of the voltage.
For better explanation, in FIG. 41, the heads 1-1, 1-2 are both shown in two separate positions, one pair for the signal system and the other pair for the drive system. Actually, however, there exist only one pair of heads 1-1, 1-2.
The base plate 5 is attached to a rotary drum (not shown) in such a manner that the heads 1-1, 1-2 are angularly spaced from each other by 180.degree. and have no step therebetween. The heads 1-1, 1-2 are rotated at, for example, a rate of 30 rotations per second (ratio corresponding to the frame frequency of a brightness signal) as the driving force of a motor 8 is transmitted to the rotary drum via a rotating shaft 9.
A magnetic tape 10 is wound around the circumferential surface of the rotary drum obliquely with respect to the rotating shaft 9 through the range of larger than 180.degree.. The magnetic tape 10 is continuously fed at a constant rate of speed (tape speed) by a capstan and a pinch roller (not shown).
Assuming that the tape speed during reproducing is 1, the tape speed during recording is 1/2. When digital data as a signal are supplied to the head 1-1 or 1-2, digital data per oblique track 11, i.e., one block of digital data corresponding to one field period of brightness signal are recorded on the tape 10. Simultaneously with this, control pulses (whose frequency is 1/2 of rotational frequency of the head 1-1, 1-2) are recorded on a control track 12 along an edge portion of the tape 10.
FIG. 41 shows a correcting circuit 13 for correcting inclination of scanning locus of the head 1-1, 1-2 during recording, a tracking servo circuit 14, a system control circuit 15 for controlling the video tape recorder into the recording mode, reproducing mode, etc., a CPU 16, a clock pulse generator circuit 17, and a frequency dividing circuit 18.
The frequency dividing circuit 18 outputs a frequency-division pulse of a frequency (corresponding to the frame frequency of a brightness signal) equal to the rotational frequency of the head 1-1, 1-2.
The correcting circuit 13 are composed of saw-tooth wave generators 19, 20, amplifiers 21, 22, an adder 23, and a voltage source 24. The tracking servo circuit 14 is composed of a phase comparing circuit 25, and amplifiers 26, 27, 28.
29, 30, 31, 32 designate interface circuits (I/O port); and 33, 34, 35, 36, 37 designate recording/reproducing change-over switches. The recording/reproducing change-over switches 33, 34, 35, 36, 37 will be connected to a junction R during recording, and will be connected to a junction P during reproducing. 38 designates a memory serving as a signal source of digital data.
In recording, the video tape recorder is rendered to the recording mode by the system control circuit 15. At that time, the tape 10 is continuously moved at a speed that is a half the speed during reproducing.
Meanwhile, the rotations of the head 1-1, 1-2 are synchronized with the recording data. Specifically, a frequency-division pulse from the frequency dividing circuit 18 is supplied to the phase comparing circuit 25, and one pulse from a pulse generating means 39 supported on the rotating shaft 9 is taken out for every rotation to the head 1-1, 1-2. This pulse is supplied to the phase comparing circuit 25 via the amplifier 26.
A signal of comparison frequency generated as a result of comparison at the phase comparing circuit 25 is supplied to the motor 8 via the amplifier 27 so that the head 1-1, 1-2 is rotated at a constant phase.
Another pulse generating means 40 is supported on the rotating shaft 9. The pulse generating means 40 outputs one pulse for every rotation of the head 11, 1-2 which pulse is displaced in phase from the pulse from the pulse generating means 39 by a 1/2 of rotation of the head 1-1, 1-2. This pulse is supplied an RS flip-flop circuit 41 via the amplifier 28. In the meantime, a pulse from the amplifier 26 is supplied to the RS flip-flop circuit 41. As a result of these inputs, a rectangular wave signal Sv is outputted, from the RS flip-flop circuit 41, so as to be "1" in the period of a 1/2 rotation Ta in which the head 1-1 is in contact with the tape 10 and so as to be "0" in the period of the other 1/2 rotation Tb in which the head 1-2 is in contact with the tape 10, as shown in FIG. 45.
This signal Sv is supplied to the CPU 16 via the interface circuit 32. The CPU 16 discriminates whether which one of the heads 1-1, 1-2 is in contact with the tape 10 depending on whether the signal Sv is "1" or "0".
The output of the system control circuit 15 is supplied to the CPU 16 via the interface circuit 31 to start recording data.
Specifically, when it enters the period Ta, one block of the data stored in the memory 38 is read according to an instruction from the CPU 16 and is then supplied to the head 1-1 via the CPU 16, the interface circuit 29, the recording amplifier 42 and the junction of the switch 33.
As a result, one block of data has been recorded as one oblique track 11A, as shown in FIG. 44.
In this case, however, since the tape speed during recording is 1/2 of that during reproducing, the track 11A would have been inclined with respect to the scanning locus of the head 1-1, 1-2 during reproducing.
During this recording, the inclination of the track 11a is corrected by the correcting circuit 13 so as to aligned with the scanning locus of the head 1-1, 1-2 during reproducing.
Specifically, when the signal Sv is supplied to the saw-tooth wave signal forming circuit 19, a saw-tooth wave signal Sa rising during every period Ta, as shown in FIG. 45. This signal Sa is supplied to the bimorph plate 3-1, which supports the head 1-1, via the amplifier 21 and the junction R of the switch 36.
Since this bimorph plate 3-1 yields depending on the polarity and level of the signal Sa, the head 1-1 will be displaced laterally of the track.
Namely, by presetting the polarity and level of the signal Sa, the track 11A to be formed by the head 1-1 can be formed so as to be aligned with the scanning locus of the head 1-1 during reproducing.
Thus a first block of data has been recorded on the tape 10 as the track 11A.
When it enters the period Tb, the head 1-2 comes in contact with the tape 10. At that time, a reverse signal Sv which is opposite to the signal Sv is taken out from the RS flip-flop circuit 41. This reverse signal Sv is supplied to the saw-tooth wave signal forming circuit 20, and as a result, rises during the period Tb, and a saw-tooth wave Sb having a waveform similar to the signal Sa will be formed. This signal Sb is supplied to a bimorph plate 3-2, which supports the head 1-2, via the adder circuit 23, the amplifier 22 and the junction R of the switch 37.
Therefore, when the head 1-2 is in contact with the tape 10 during the period Tb, the head 1-2 scans the tape 10 in parallel to the track 11A.
During that time, since the tape speed is 1/2 of that during reproducing, the head 1-2 scans the tape 10 between the previous track 11A and the next track 11B (which is not yet formed).
Then, a predetermined d.c. bias voltage is taken out from the d.c. voltage source 24 and is supplied to the bimorph plate 3-2 via the adder circuit 23, the amplifier 22 and the line of switch 37. As a result, since the bimorph plate 3-2 yields to an extent corresponding to the d.c. bias voltage, the head 1-2 scans the track 11A while the head 1-2 is in contact with the tape 10.
During the period Tb, a reproducing signal of the track 11a which the head 1-1 recorded during the previous period Ta, can be obtained from the head 1-2.
This reproducing signal is supplied to a switch circuit 44 via a reproducing amplifier 43. At the same time, a signal Sv is supplied to the switch circuit 44. The switch circuit 44 is controlled according to this signal Sv, and as a result, the reproducing signal is supplied to the CPU 16 via the interface circuit 30.
In the CPU 16, this reproducing signal is compared with the data in the memory 38.
Thus, the data recorded as the track 11A by the head 1-1 during the period Ta are reproduced by the head 1-2 during the period Tb, and are compared with the original data.
As a result of this comparison, if there is no error in recording on the track 11A, the next block of data is recorded as the track 11B during the following period Ta by the head 1-1. Further, in the subsequent period Tb, the track 11B is reproduced by the head 1-2 and is then compared with the original data.
Thus, in the period Ta, one block of data is recorded as the track 11 by the head 1-1, and in the subsequent period Tb, the track 11 recorded in the previous period Ta is reproduced by the head 1-2. Then the state of recording of the track 11 is confirmed, and operation is repeated in the absence of any error in recording.
Meanwhile, if there is found an error in the records on track 11A as a result of this comparison during the period Tb, one block of data to be recorded on the track 11A is recorded on the track 11B during the next period Ta, and in the subsequent period Tb, this track 11B is reproduced to confirm the records.
In the absence of any error in the records of the track 11B, the next block of data is recorded on the track 11 in the next period Tc.
In the presence of any error in recording, the track 11 is skipped and the data are recorded on the track 11 in order as the latter is shifted.
As described above, data are progressively recorded on the tape 10 one block to another as the track 11 while recording and conformation of the recording are conducted alternately.
During this recording, the frequency-division pulse from the frequency dividing circuit 18 is further supplied to a frequency dividing circuit 45 so as to be a 1/2 frequency pulse (having a frequency which is 1/2 the rotational frequency of the head 1-1, 1-2). This pulse is supplied to a head 47 via a recording amplifier 46 and the junction R of the switch 35 and is recorded on the tape 10 as the track 12.
During reproducing, the bimorph plate 3-1, 3-2 is rendered to assume a reference voltage by the switch 36, 37 so that the head 1-1, 1-2 is fixed at a reference position. By the system control circuit 15, the tape 10 is continuously fed at a speed double the speed during recording.
At that time, a pulse (a control pulse) having a frequency equal to the rotational frequency of the head 1-1, 1-2 is reproduced from the track 12 by the head 47. This pulse is supplied to the phase comparing circuit 25 via the junction P of the switch 35, a reproducing amplifier 48 and the junction P of the switch 34.
The output of the phase comparing circuit 25 is supplied to the motor 8 via the amplifier 27; that is, by the result of phase comparison of the pulses in the comparing circuit 25, the motor 8 is controlled.
Thus, the tracking servo control of the head 1-1, 1-2 with respect to the track 11 is performed, and the heads 1-1, 1-2 alternately scan the track 11, so that reproducing signals can be obtained alternately from the heads 1-1, 1-2.
The reproducing signal of the head 1-1 is supplied to the switch circuit 44 via the junction P of the switch 33 and a reproducing amplifier 49. On the other hand, the reproducing signal of the head 1-2 is supplied to the switch circuit 44 via the reproducing amplifier 43. From the switch circuit 44, reproducing signals of the track 11 are taken out successively. The reproducing signal is supplied to the CPU 16 via the interface circuit 30, and is stored in, for example, the memory 38.
With this prior art, for one second, for example, only the signal whose quantity corresponds to 30 field period of the brightness signal can be processed. Therefore it is impossible to process, with real time, signals such as television signals that continue 60 fields in one second.
FIG. 46 shows another prior art magnetic recording and reproducing apparatus disclosed in, for example, Japanese Patent Laid-Open Publication No. 133573/1985. In FIG. 46, 101-1 and 101-2 designate a pair of magnetic heads, and 102 designates a rotary drum. The magnetic heads 101-1, 101-2 are mounted on the peripheral edge of the rotary drum 102 and are angularly spaced from each other by 180.degree..
110 designates a magnetic tape, and 114 designates a mechanism control circuit. The mechanism control circuit 114 controls the number of rotations of the rotary drum 102 and the feeding of the magnetic tape 110.
A low-pass filter (hereinafter called "LPF") makes a band restriction for sampling the inputted recording video signal. An A/D converter 151 samples the band-restricted recording video signal. An encoder 152 encodes digitized recording video data so that an error which occurred when the data are magnetically recorded and reproduced can be corrected. A modulator 153 encodes the encoded recording video data so as to be optimum data suitable for magnetic recording and reproducing. A head amplifier 142 amplifies the recording video data signal during recording and drives the magnetic heads 101-1, 101-2.
A reproducing head amplifier 143 amplifies the reproducing signal reproduced by the magnetic heads 1-1, 1-2 during reproducing. A demodulator 154 decodes the reproducing signal in the manner reverse to the encoding in the modulator 153. A decoder 155 detects and corrects any error in the decoded data. A D/A converter 156 reproducing video data whose error has been corrected by the decoder in an analog form. An LPF 157 restricts the reproducing video signal to a video signal band and outputs the restricted signal.
A self-recording-and-reproducing/dubbing changeover switch (hereinafter called "change-over switch") 158 is disposed between encoder 152 and the modulator 153. The change-over switch 158 makes a change-over between the self-recording-and-reproducing mode and the dubbing mode and is controlled by a change-over signal. By this change-over action of the change-over switch 158, the dubbing input signal or the output of the encoder 152 is inputted to the modulator 153. In the meantime, the output of the demodulator 155 is supplied to the D/A converter 156 and is outputted to the exterior as a dubbing output signal.
A synchronizing signal from an external apparatus is inputted to the mechanical control circuit 114 to synchronize the mechanical control circuit 114 with the external apparatus. The mechanical control circuit 114 outputs an exterior synchronizing signal. This exterior synchronizing signal is a reference signal for controlling the number of rotations of a rotary drum and the feed of a tape.
FIG. 47 is a data diagram showing one example of operation of the error correcting encoder 152. In FIG. 47, D(1, 1), D(1, 2), D(2, 1), D(2, 2), . . . D(8, 1), D(8, 2) designate information data; C(1, 1), C(1, 2), C(1, 3), C(2, 1), C(2, 2), C(2, 3) . . . C(9, 1), C(9, 2), C(9, 3), error detection data; P.sub.H (1, 3) , PH (2, 3) . . . P.sub.H (9, 3) , horizontal parity data; and P.sub.V (9, 1) , P.sub.V (9, 2), vertical parity data.
FIG. 48 shows, of the data shown in FIG. 47, the data in which errors occurred. Here assume that the error data exist in the second of D(2, 1), the fifth of D(2, 1), the fifth of D(2, 2), the fifth of D(6, 1) and the fifth of P.sub.H (6, 3).
FIG. 49 shows the data in which errors occurred as shown in FIG. 48 were not corrected by the decoder 155. Namely, assume that the errors about the fifth of D(2, 1) and fifth of D(6, 1) of the data shown in FIG. 49 could not be corrected also by the decoder 155.
FIG. 50 is a wiring diagram showing the dubbing operation in which a pair of prior art magnetic recording and reproducing apparatus are used. In FIG. 50, 159 designates a master magnetic recording and reproducing apparatus (hereinafter called "master deck"), and 160 designates a slave magnetic recording and reproducing apparatus (hereinafter called "slave deck") .
In operation, in the ordinary self-recording-and-reproducing mode, a recording video signal is supplied to the LPF 150 where its band is restricted, and the band-restricted recording video signal is sampled by a frequency two times higher than the video signal band by the A/D converter 151. Generally, in NTSC system, the video signal band is about 4.5 MHz, and it is necessary to sample the video signal by a frequency higher than 9 MHz according to Nyquist's theorem. Since a color signal is transmitted as a carrier of 3.58 MHz is perpendicular-two-phase modulated, it is customary to set the sampled frequency as a multiple integer of 3.58 MHz in view of beat interference with the sampled frequency. From these relations, very occasionally the sampled frequency is set to 3.multidot.f.sub.sc (f.sub.sc stands for a carrier frequency of 3.58 MHz, and 3.multidot.f.sub.sc stands for about 10.7 MHz) and 4.f.sub.sc (about 14.3 MHz).
Digitized recording video data are encoded by the encoder 152 so that errors occurred during magnetic recording and reproducing can be corrected, and the data are then transferred to the change-over switch 158.
The change-over switch 158 here assumes the self-recording-and-reproducing mode and hence is connected to the self-recording-and-reproducing side, namely, the side of the encoder 152.
Therefore, the encoded data are encoded by the modulator 153 so as to be the optimum data suitable for magnetic recording and reproducing. This encoding system is exemplified by NRZ and NRZI systems. The modulated recording video data are amplified by the recording head amplifier 142 and are then recorded on the magnetic tape 110 by the magnetic heads 101-1, 101-2. The mechanism control circuit 114 controls the number of rotation of the rotary drum 102 at a constant rate and controls the feed of the tape 110 at a constant rate. As a result, the recording video data are recorded on the magnetic tape 110 by helically scanning.
In reproducing, the signal reproduced by the magnetic heads 101-1, 101-2 is amplified by the reproducing head amplifier 143. The amplified signal is decoded by the demodulator 154, and the decoder 155 corrects and detects errors in the reproducing data. The data in which errors have been corrected and detected are converted to analog signals by the D/A converter 156, are restricted in band by the LPF 157, and are outputted as a reproducing video signal.
The error correcting method by using the encoder 152 and the decoder 155 will now be described with reference to FIGS. 47 through 49. The encoder 152 forms error detection data C(m, n) (where m and n are integers satisfying 1&lt;m&lt;8, and 1&lt;n&lt;2) as redundant data, from which errors are to be detected, with respect to information data D(m, n) digitalized by the A/D converter 151.
The horizontal parity P.sub.H (1, 3) is the parity composed of D(1, 1) and D(1, 2). The parity of l-th data of D(1, 1), and l-th data of D(1, 2) is l-th data of P.sub.H (1, 3). Likewise, P.sub.H (m, 3) is the parity composed of D(m, 1) and D(m, 2), and C(m, 3) is the error detection data of P.sub.H (m, 3).
The vertical parity P.sub.V (9, 1) is the parity composed of D(1, 1), D(2, 1) . . . D(8, 1). l-th data of P.sub.V (9, 1) are the parity composed of l-th data of D(1, 1), D(2, 1) . . . D(8, 1). Likewise, P.sub.V (9, 2) is the parity composed of D(1, 2), D(2, 2) . . . D(8, 2).
P.sub.H (9, 3) is the parity composed of P.sub.V (9, 1) and P.sub.V (9, 2), and C(9, 1), C(9, 2) and C(9, 3) are the respective error detection data of P.sub.V (9, 1), P.sub.V (9, 2) and P.sub.H (9, 3). In this example, each of D(m, n) , P.sub.H (m, 3) and P.sub.V (9, n) is composed of 6 bits, and C(m, n) is composed of 2 bits.
As shown in FIG. 48, in the presence of errors respectively occurred in the reproducing data D(2, 1), D(2, 2), D(6, 1), P.sub.H (6, 3), when a horizontal parity is formed from the reproduced D (2, 1) and D (2, 2), an error exists in the second bit of D(2, 1). Therefore the second bit of the formed horizontal parity is different from the second bit of P.sub.H (2, 3). However, since the fifth bit of D(2, 1) and the fifth bit of D(2, 2) have errors, the formed horizontal parity and the fifth bit of P.sub.H (2, 3) are equal to each other. As the result of detection of errors in D(2, 1) and D(2, 2), only errors are corrected from the P.sub.H (2, 3) and the formed horizontal parity.
Likewise, an error is detected in D(6, 1), and no error is detected in D(6, 2). Therefore, if a horizontal parity is formed from the reproduced D(6, 1) and D(6, 2), there is a difference in the fifth bit from the original P.sub.H (6, 3). Since the fifth bit of P.sub.H (6, 3) also has an error, no error can be corrected.
Then, when a vertical parity is formed from the reproduced D(1, 1), D(2, 1), D(3, 1) . . . D(8, 1), both D(2, 1) and D(6, 1) have errors at their fifth bits. Therefore, this vertical parity will be identical with the fifth data of P.sub.V (9, 1) so that correction is impossible.
If the vertical parity is formed from the reproduced D(1, 2), D(2, 2), D(3, 2) . . . D(8, 2), the fifth data are different from the fifth data of Pv(9, 2) due to the error. As a result of this and the error detection of D(2, 2), the error is corrected. Similarly, the error in P.sub.H (6, 3) is also corrected. But the errors in the fourth data of D(2, 1) and D(6, 1) will remain uncorrected, as shown in FIG. 49.
The manner of dubbing by using this magnetic recording and reproducing apparatus will now be described.
In FIG. 50, the dubbing output signal (the output of the decoder 155) of the master deck 159 is inputted to the dubbing-side terminal of a change-over switch 258 as a dubbing input signal. Further, the external synchronizing signal, which is the output of the mechanism control circuit 114 of the master deck 159, is inputted to the mechanism control circuit 214 of the slave deck 16 as a synchronizing signal.
From the master tape 110 mounted on the master deck 159, recording video data are reproduced by the magnetic heads 101-1, 101-2. The reproduced data are demodulated by the demodulator 154, and any error in the reproduced data is detected and corrected by the decoder 155. The data in which errors have been corrected are transferred to the slave deck 160 as the dubbing output signal in the form of digital video data. The slave deck 160 again encodes the transferred digital video data to a modulator 253 and records the encoded data on a slave tape 210. Thus dubbing from the master tape 110 to the slave tape 210 has been performed.
Assume that the errors such as shown in FIG. 48 occurred during reproducing the master tape 110, that dubbing was performed with part of the errors uncorrected and that no error occurred during reproducing the slave tape 210. At that time, the encoder of the slave deck 160 detects that the errors occurring in D(2, 1) and D(6, 1) so that the horizontal parity formed from the reproduced D(2, 1) and D(2, 2) will be different from the fifth data of P.sub.H (2, 3). Therefore, the error of D(2, 1) will be corrected from P.sub.H (2, 3) and from the horizontal parity formed from the reproduced D(2, 1) and D(2, 2), and likewise, the error of D(6, 1) also will be corrected.
In editing and dubbing, assuming that no new error occurs after the second generation, correction in the horizontal parity and correction in the vertical parity will be repeated as the generation is transferred from the second to the third generation. Therefore the errors occurring in the first generation will continue to be reduced to a predetermined rate. Practically, however, a new error would occur everytime the generation is transferred, thus reducing the rate of minimizing the rate of error occurrence.
Generally, in recording and reproducing video signals for self-recording-and-reproducing, dubbing, etc., data will be processed in blocks, such as units of video signal fields or frames so that the data will be recorded on the track of the magnetic tape in units of blocks.
With this prior magnetic recording and reproducing apparatus, in order to maintain a low rate of error occurrence, dubbing can be performed only at the rate of ordinary recording and reproducing, thus taking a long period of time.
FIG. 51 shows the location of magnetic heads in a prior art magnetic recording and reproducing apparatus exemplified by Japanese Patent Laid-Open Publication No. 165801/1986. FIG. 52 shows a track pattern of recording onto a magnetic tape by the magnetic heads.
In FIG. 51, a pair of first magnetic heads 301-1, 301-2 are arranged on the peripheral edge of a rotary drum 302 and are angularly spaced from each other by 180.degree., and likewise, a pair of second magnetic heads 301-3, 301-4 are arranged on the peripheral edge of the rotary drum 302 and are angularly spaced from each other by 180.degree.. The second magnetic heads 301-3, 301-4 are angularly spaced from the first magnetic heads 301-1, 301-2, respectively, by 90.degree..
In FIG. 52, the magnetic tape 310 is fed in the direction of an arrow R. 311-1 designates a track recorded by the first magnetic head 301-1; 311-2, a track recorded by the second magnetic head 301-3; 311-3, a track recorded by the first magnetic head 301-2; and 311-4, a track recorded by the second magnetic head 301-4. These four recording tracks 311-1 through 311-4 constitute one frame of recording data.
FIG. 53 is a block diagram showing recording signal processing system when digitally recording 2-channel video signals simultaneously in the arrangement and track pattern of the magnetic heads of FIGS. 51 and 52.
A first low-pass filter (hereinafter called "first LPF") 350 performs a band restriction to sample a first video signal. A second LPF 350-2 performs a band restriction of a second video signal.
A first A/D converter 351-1 samples the first video signal, and a second A/D converter 351-2 samples the second video signal.
A first encoder 352-1 encodes digital data from the first A/D converter 351-1 by adding an error correcting code thereto. A second encoder 352-2 encodes digital data from the second A/D converter 351-2 in the same manner. A first memory 338-1 is used in encoding by the first encoder 352-1, and a second memory 338-2 is used in encoding by the second encoder 352-2. A first modulator 353-1 encodes the digital data, which were encoded by the first encoder 352-1, into optimum recording codes suitable for magnetic recording and reproducing. A second modulator 353-2 encodes the digital data, which were encoded by the second encoder 352-2, into optimum recording codes suitable for magnetic recording and reproducing.
A first recording head amplifier 342-1 drives the first magnetic heads 301-1, 301-2 based on the output of the first modulator 353-1. A second recording head amplifier 342-2 drives the second magnetic heads 301-3, 301-4 based on the output of the second modulator 353-2.
FIG. 54 is a diagram showing the arrangement of magnetic heads and the operating period of each magnetic head for recording, with respect to the first and second channel recording data. The first and second channels correspond to the respective outputs of the first and second modulators 353-1, 353-2.
In operation, in two-channel recording and reproducing, the magnetic tape 310 is fed at a speed two times higher than ordinary. At that time, the first magnetic heads 301-1, 301-2, which are arranged on the rotary drum 302 and are angularly spaced from each other by 180.degree., record and reproduce a video signal. Meanwhile, the second magnetic heads 301-3, 301-4 record and reproduce an audio signal, a different video signal or the like.
In this case, the recording track pattern on the magnetic tape 310 by the first and second magnetic heads 301-1, 301-2, 301-3, 301-4 is shown in FIG. 52. Specifically, the track 311-1 is recorded by one (301-1) of the first magnetic heads 301-1, 301-2, and the track 311-2 is recorded by one (301-3) of the second magnetic heads 301-3,301-4. Likewise, the track 311-3 is recorded by the other (301-2) of the first magnetic heads 301-1, 301-2, and the track 311-4 is recorded by the other 301-4 of the second magnetic heads 301-3, 301-4.
Accordingly, two pieces of information are recorded at every rotation of the rotary drum 302.
The mode of operation of the recording signal processing system for, for example, digitally recording two-channel video signals will now be described. Although there is no illustration of the audio signal processing system, audio signals like the video signals are digitally recorded.
In FIG. 53, the first and second channel video signals are restricted in band so that the first and second LPFs 350-1, 350-2 allow the video signal band to pass. Then, the video signals are sampled at a frequency more than two times higher than the video signal band by the first and second A/D converters 351-1, 351-2.
Generally, in a NTSC system, the video signal band is about 4.5 MHz, and it is necessary to sample the video signal by a frequency higher than 9 MHz according to Nyquist's theorem. Since a color signal is transmitted as a carrier of 3.58 MHz is perpendicular-two-phase modulated, it is customary to set the sampled frequency multiple by an integer over 3.58 MHz in view of beat interference with the sampled frequency. From these relations, very occasionally the sampled frequency is set to 3.multidot.f.sub.sc (f.sub.sc stands for a carrier frequency of 3.58 MHz, and 3.multidot.f.sub.sc stands for about 10.7 MHz) and 4.f.sub.sc (about 14.3 MHz).
The thus digitized recording video data are encoded by the first and second encoders 352-1, 352-2 such that the errors occurring during magnetic recording and reproducing can be corrected. Here the first and second memories 338-1, 338-2 are used in encoding.
Then the encoded data are encoded by the first and second modulators 353-1, 353-2 so as to be the optimum data suitable for magnetic recording and reproducing. This encoding system is exemplified by NRZ and NRZI systems.
Subsequently, the modulated recording video data are recorded on the magnetic tape 310. Specifically, the first and second channel digital data are recorded by the first magnetic heads 301-1, 301-2 and the second magnetic heads 301-3,301-4 via the first and second recording head amplifiers 342-1, 342-2, respectively.
Here the arrangement of the magnetic heads of the two-channel recording data are shown in FIG. 54. Specifically, DATA1-1 of the first channel is recorded on the track 311-1 by the first magnetic head 301-1, while DATA1-2 of the first channel is recorded on the track 311-3 by the first magnetic head 301-2. Likewise, DATA2-1 of the second channel is recorded on the track 311-2 by the second magnetic head 301-3, while DATA2-2 of the second channel is recorded on the track 311-4 by the second magnetic head 301-4.
By the foregoing operation, two-channel video signals can be recorded simultaneously. Also in reproducing, two-channel video signals can be reproduced simultaneously by tracing the track.
With this prior art magnetic recording and reproducing apparatus, in order to record two-channel video signals, it is necessary to add two magnetic heads. Also, two signal processing circuits are necessary. Further, it is impossible to do one-channel recording, while reproducing at the other channel.
Insert editing is writing and editing a part of an already recorded track with a different signal and is an effective function in VTR (video tape recorder) for recording and reproducing video and audio signals. A four-frequency pilot method is adopted for the servo method of 8 mm video using an 8 mm tape. This prior art insert editing method is exemplified by Japanese Patent Laid-Open Publication No. 79550/1985.
In the prior magnetic recording and reproducing apparatus using the pilot signal method, in addition to two ordinary magnetic heads arranged on the peripheral edge of the rotary drum and angularly spaced from each other by 180.degree., at least one magnetic head is used so that the track pattern will be continuous and uniform during insert editing.
The arrangement and construction of the heads of this fourth prior art is similar to those of the third prior art.
FIG. 55 shows a circuit of a rotary-head-type VTR to which the magnetic recording and reproducing apparatus is incorporated. In FIG. 55, a first circulating frequency generator 461 generates four signals of different frequencies one for each field, circulating four fields as one cycle, according to the head switching pulses inputted to an input terminal 462.
For example, in recording video signals by NTSC (National Television System Committee) method, these four frequencies should be selected as follows: f.sub.1 =f.sub.osc /58, f.sub.2 =f.sub.osc /50, f.sub.3 =f.sub.osc /36, and f.sub.4 =f.sub.osc /40, where f.sub.osc =378 fh (fh: frequency of horizontal synchronizing signal). The output of this frequency generator 461 is inputted to the input terminal 463 and is superposed with the modulated video signal by an adding circuit 464. This superposed signal is applied to the magnetic heads 401-1, 4-1-2 via a recording amplifier 442, a switch 465 and a rotary transformer 406, and is recorded on the magnetic tape. The recording pattern is circulating from F1 to F4, as shown in FIG. 56.
Then the ordinary reproducing will now be described.
Regarding the output of the reproducing amplifier 443, a low-pass filter (hereinafter called "LPF") 467 cancels video signal components and extracts pilot signal components. The pilot signal components extracted by the LPF 467 and the output of the circulating frequency generator 461 are inputted to a mixer 468. The output of this mixer 468 is inputted to a first band-pass filter (hereinafter called "BPF") 11 or a second BPF 12 to obtain a differential frequency signal component between the signal frequency of the output of the circulating frequency generator 461 and the frequency of pilot signal component of the output of the LPF 467.
In the case of video signals in NTSC method, since f.sub.osc .apprxeq.5.95 MHz, f.sub.1 .apprxeq.102 KHz, f.sub.2 .apprxeq.119 KHz, f.sub.3 .apprxeq.165 KHz, and f.sub.4 .apprxeq.149 KHz. Therefore f.sub.2 -F.sub.1 .apprxeq.f.sub.3 -f.sub.4 .apprxeq.16.5 KHz, and f.sub.4 -f.sub.1 .apprxeq.f.sub.3 -f.sub.2 .apprxeq.46.5 KHz. Consequently, the pass band of the first BPF 469-1 and the pass band of the second BPF 469-2 are selected to be around 16.5 KHz and around 46.5 KHz, respectively.
As shown in FIG. 56, when the magnetic head 401-1 is tracking the track F2, a signal having an amplitude proportional to the magnitude of the pilot signal (frequency f.sub.2) component of the track F1 will be obtained from the first BPF 469-1, and a signal having an amplitude proportional to the magnitude of the pilot signal (frequency f.sub.4) component of the track F4 will be obtained from the second BPF 469-2.
The outputs of the first and second BPFs 469-1, 469-2 are envelope-detected by first and second detectors 470-1, 470-2, respectively. The outputs of the first and second detectors 470-1, 470-2 are supplied to a subtractor 471 so that a voltage level corresponding to the amount of lateral displacement of the magnetic head 401-1 from the center of the track in FIG. 56 is obtained as the output of the subtractor 471.
As is apparent from the frequencies f.sub.1, f.sub.2, f.sub.3, f.sub.4 and the recording pattern of FIG. 56, the polarity of the output of the subtractor 471 with respect to the displacement of the magnetic head 401-1 from the center of the track when the magnetic head 401-1 is tracking F1 or F3 will be opposite to that when the magnetic head 401-1 is tracking F2 or F4. Therefore, by selectively synchronizing the output of the subtractor 471 or the signal, which is obtained by inverting the output of the subtractor 471 by an inverting amplifier 472, with the head switching pulses by a switch 473, an output voltage proportional to the amount of displacement of the magnetic head 201-1 can be obtained from an output terminal 474. The signal obtained from the output terminal 474 is feedbacked to a capstan motor (not shown) so that good tracking can be achieved.
The construction and operation of this prior apparatus for insert editing will now be described.
A switch 475 serves to allow the reproducing output of the magnetic head 201-3 or 201-4 to be supplied to the reproducing amplifier 443 during insert editing. A delay circuit 476 shifts the head switching pulses in phase by 90.degree.. A second circulating frequency generator 477 generates signals of the above described frequencies f.sub.1, f.sub.2, f.sub.3 and f.sub.4 based on the output of the delay circuit 476. A switch 478 serves to allow the output of the second circulating frequency generator 477 to be supplied to the mixer 468 during insert editing. A switch 479 serves to selectively allow the output of the first or second detector 470-1, 470-2 to be supplied to an amplifier 480 for every field based on the output of the delay circuit 476. A switch 481 serves to allow the output of the amplifier 480 to be supplied to the output terminal 474 during insert editing.
During insert editing, the output of the first circulating frequency generator 461 is superposed over a video signal inputted from the input terminal 463. This signal is applied to the magnetic heads 401-1, 401-2 via the recording amplifier 442, the switch 465 and a rotary transformer 466 and is recorded on the magnetic tape 410.
On the other hand, the signal on the magnetic tape 410 is reproduced by the magnetic head 401-3, 401-4 and is supplied to the reproducing amplifier 443 via the rotary transformer 466 and the switch 475.
For starting the signal recording in insert editing, first the tape feed in ordinary reproducing is controlled, and after entering the synchronizing control, it is switched to the insert editing mode at a desired recording starting point. At that time, the positional relation between the recording pattern on the magnetic tape 410 and each magnetic head 401-1 through 401-4 is shown in FIG. 56, for example. Specifically, the magnetic head 401-1 is disposed on the leading end of the track F1, and the magnetic head 401-2 is disposed on the trailing end of the track F4. Therefore, the magnetic head 401-3 is located centrally of the track and on the boundary line between the track F4 and the track F1.
The delay circuit 476 shifts the head switching pulses in phase by 90.degree. so that the switching position of the magnetic head 401-3 or 401-4 will be aligned with the head switching position of the magnetic head 401-1 or 401-2 laterally of the tape. Further, the delay circuit 476 generates the signals of frequencies f.sub.1,f.sub.2, f.sub.3 and f.sub.4 in a predetermined order from the second circulating frequency generator 477.
In the magnetic head position of FIG. 56, assume that the frequency f.sub.4 is generated from the second circulating frequency generator 477. During that time, the first circulating frequency generator 461 generates a frequency, changing over from the frequency f.sub.4 to the frequency f.sub.1.
The signal reproduced from the magnetic head 401-3 includes the pilot signal component of the frequency f.sub.1 corresponding to 1/2 of the head width, and the component of the frequency f.sub.4 corresponding to 1/2 of the head width. In the LPF 467, the two pilot components are extracted and are supplied to the mixer 468.
On the other hand, since the second circulating frequency generator 477 generates the frequency f.sub.4, the signal such that the differential frequency component has an amplitude corresponding to 1/2 of the head width is obtained from the second BPF 469-1.
When the magnetic head 401-4 is located on the boundary line between the track F1 and the track F2 in FIG. 56, namely, when the magnetic head 401-1 is located above the track F1 of the tape or when the magnetic head 401-2 is located under the track F2 of the tape, the second circulating frequency generator 477 generates the signal of the frequency f.sub.1. At that time, the signal of an amplitude proportional to the head width on the track F2 with a differential frequency between f.sub.1 and f.sub.2 is obtained from the first BPF 469-1.
By controlling the frequency from the second circulating frequency generator 477 by the signal, which is obtained by shifting the head switching pulse (from the delay circuit 476) in phase by 90.degree., when the magnetic head 401-3 is located on the boundary line between the track F4 and the track F1 or on the boundary line between the track F2 and the track F3, the signal of an amplitude proportional to the displacement of the magnetic head 401-3 from the boundary line can be obtained from the second BPF 469-2. Further, when the magnetic head 401-4 is located on the boundary line between the track F1 and the track F2 or on the boundary between the track F3 and the track F4, the signal of an amplitude proportional to the displacement of the magnetic head 401-4 can be obtained from the first BPF 469-1.
Therefore, by selecting the output of the first detector 470-1 or the second detector 470-2 by operating the switch 479 according to the output of the delay circuit 476, a voltage proportional to the displacement of the magnetic head 401-3 or 401-4 from the boundary line can be obtained. This voltage equivalently represents a voltage value proportional to the displacement of the magnetic head 401-1 or 401-2 from the track. This signal is supplied to the amplifier 480 where a suitable DC offset and an amplification gain are given to the signal, and the resulting signal is supplied to the output terminal 474 via the switch 481.
Assuming that the output of the second circulating frequency generator 477 is fixed at the frequency f.sub.1, the output voltage of the output terminal 474 with respect to the displacement of the magnetic head 401-4 in the longitudinal direction of the tape varies as shown in FIG. 57. In FIG. 57, as this output voltage is integrated in the longitudinal direction of the tape, an integration value will be V.sub.1. The output voltage at a desired tracking position is V.sub.0 so that a lock range when a control loop is provided will apparently be subjected to a large restriction. Consequently, if synchronization is taken in the ordinary reproducing mode before starting the insert editing, the control ability for small signal components is adequate even when entered the insert editing mode. Therefore, if synchronization is taken in the ordinary reproducing mode, a uniform, continuous recording pattern can be obtained also during insert editing.
With this prior art magnetic recording and reproducing apparatus, it is necessary to provide at least one magnetic head in addition to the ordinary recording and reproducing heads, thus increasing the cost of production and making it difficult to reduce the size of the rotary drum.
FIG. 58 shows one example of a tape format for a magnetic recording reproducing apparatus which enables reciprocating reproducing, the tape format being described in, for example, a book "NHK Home Video Description" (page 213) issued from Japan Broadcasting Association (Nippon Hoso Kyokai).
A magnetic tape 510 is 1/2 inch wide, on which surface each track is formed in the following format. Specifically, a video track 511-V1 is a track on and from which video signals are to be recorded and reproduced in the direction of forward tape feed; an audio track 511-A1 is a track on and from which audio signals are to be recorded and reproduced in the direction of forward tape feed; a video track 511-V2 is a track on and from which video signals are to be recorded and reproduced in the direction of reverse tape feed; and an audio track 511-A2 is a track on and from which audio signals are to be recorded and reproduced in the direction of reverse tape feed.
The object of this prior art apparatus using such a tape format is to enable long-time recording and recording and reproducing band of audio signals by reciprocatingly using the magnetic tape 510.
By multiplying the rate of magnetic tape feed about two times, the tape format of FIG. 58 can be formed within a width (1/4 inch) which is a half of the magnetic tape 510 having a 1/2-inch width as used in the VHS method or such. The formed tape format includes the video tracks 511-V1, 511-V2 for recording and reproducing in the helically scanning method and the audio tracks 511-A1, 511-A2 for recording and reproducing on linear tracks.
For example, using the lower half (1/4 inch) of the magnetic tape 510 during forward tape feed, the video signals are recorded on the video track 511-V1, and the audio signals are recorded on the audio track 511-A1.
Then, When the direction of the magnetic tape feed becomes relatively reversed by turning the magnetic tape 510 inside out, the video signals and the audio signals are recorded on the video track 511-V2 and the audio track 511-A1, using the lower half (1/4 inch) of the magnetic tape 510.
Concerning the recording and reproducing of video signals, this prior system is equivalent to only one-way recording and reproducing of the VHS method, but the audio signals for recording and reproducing to the linear track is increased in relative speed to improve the recording and reproducing band of the audio signals.
With this prior magnetic recording and reproducing apparatus, it is necessary to turn the magnetic tape inside out when the direction of tape feed is switched from the forward to the reverse and vice versa. Also it is impossible to switch the tape feed direction instantly.